This invention relates primarily to innovations in shrimp mariculture wherein the fertilization rate of the shrimp eggs is increased and regulated.
One of the most important fishery products among the crustacea that can be utilized as a food resource for human consumption is the ocean shrimp, particularly the shrimp of the genus, Penaeus. This fact has been appreciated, and as a result, cultivation of penaeid shrimp on a commercial scale has been undertaken. However, there are many problems attendant to conventional methods of raising shrimp and to shrimp mariculture operations in general. One of which is obtaining a suitable stock of fertilized eggs on which to base a continuous grow-out operation. Some species of the genus Penaeus have matured and mated naturally in captivity, but this has been accomplished on a generally indeterminate basis and no reliance can be given to this method of supplying fertile eggs to a commercial shrimp farm. Therefore, in order to obtain the required shrimp eggs for a shrimp farm grow-out operation it is necessary to capture gravid female shrimp in their natural environment and transfer them to the shrimp farm hatchery. The shipment of such gravid shrimp requires rather close controls to monitor the refrigeration or cooling conditions and the oxygen supply of the shrimp to insure their viability and to inhibit premature spawning. The aforementioned handling process is suitable for those commercially valuable species of penaid shrimp which mate prior to egg development, for example, the brown or grooved species. The groove refers to an axial, posterior indentation along the rostrum of the shrimp. These shrimp have distinctive reproductive characteristics which facilitate the handling of the gravid females. At the time the female brown shrimp moults its exoskeleton, it is vulnerable to mating. It is not understood by researchers in the art if this moult takes place for growing or mating purposes. However, usually before a replacement exoskeleton is formed, the female mates with a male with mature spermatophore or sperm packet. The male inserts the spermatophore into a receptacle on the female called the thelycum, which is located between the fifth pair of walking legs or pereiopods. The female carries the sperm during the egg development and maturation. When the female brown shrimp spawns the mature eggs into the sea water from the ovipores at the base of the third pair of walking legs, the sperm is simultaneously released into the sea water, where fertilization occurs. Seldom is a female brown shrimp caught in the ocean with mature eggs, which has not mated.
Another commercially valuable shrimp, the white or non-grooved species of the genus Penaeus, has different reproductive characteristics than the brown or grooved species. The white shrimp species generally respond better to conventional culture conditions, and therefore are more desirable for use in shrimp farming. However, differences in reproductive mode makes it more difficult to obtain fertile eggs. Egg development and maturation in the female white shrimp occur prior to mating. The thelycum or sperm receptacle of the female white shrimp is non-functional and possibly vestigial. The exoskeleton of the female remains attached and hardened during mating which usually occurs about four to twelve hours prior to spawning. The male attaches a sperm packet, commonly referred to as a spermatophore, onto the ventral side of the female between the third and fourth pairs of walking legs. The spermatophore is a chitinous, bananna shaped pouch with two wing-like lateral extensions, and is held in place by a white glutenous material. The sperm mass moves forward inside the spermatophore and is deposited as a jelly-like mass at the base of the third pair of walking legs near the vicinity of the ovipores. When the female white shrimp spawns, the jelly-like mass of sperm dissolves into the sea water simultaneously and fertilizes the eggs. Thus, if wild female white shrimp with mature ovaries are captured in the trawling gear of a shrimp boat, there is a possibility that all of them will not be mated. In fact, it has been the inventor's personal experience while trawling for white shrimp, that for every mated wild female white shrimp with mature ovaries caught, there are captured from one to eight unmated females with mature eggs. This statistic may be due to the random natural mating characteristics of the white shrimp or possibly due to the spermatophore becoming disengaged from the female upon its capture in a trawl.
There is a definite need for a method of artificially inseminating shrimp to allow the selection of desired individuals for mating and to obtain a regulated supply of fertilized eggs for the shrimp farming industry.